Unlock the iphone desktop, find the Settings in the desktop, and enter the Settings interface.
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In the Settings screen, tap the battery option.
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In the battery screen, click to find the battery Health option.
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In the Battery Health homepage, click on the optimized battery charging option, turn on the optimized battery charging function, and automatically power off after the phone is fully charged.
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An iPhone running iOS7 or higher will automatically power off after a full charge.